Controlled-environment communication systems are telecommunication systems designed to enable members within a controlled-environment facility to communicate with parties outside of that facility. These systems allow telecommunications activities for the populations of those facilities to be highly regulated. They are designed with security measures and apparatus that enable administrators of such facilities to set policies for allowed and disallowed activity, to monitor voice calls to detect members within the facility engaging in disallowed activities, and also to bill parties on the call as appropriate. These systems are designed for many contexts in which monitoring of telecommunications activity is desirable, such as health facilities, military facilities, and correctional facilities such as prisons. The prison application has an especially urgent need for strong security measures and apparatus. In the prison context, a controlled-environment communication system is commonly referred to as an inmate communication system (ICS).
Prison inmate communication is highly circumscribed because of the potential for abuse. Inmates have been known to use inmate communication systems in the past to engage in illicit activity outside of the prison, threaten parties of interest such as judges, attorneys, and witnesses, and communicate with inmates in other prison facilities about possibly illegal activity. As such, several security measures have been developed for use with these systems over the past several decades. Combinations of several features such as personal identification number (PIN) entry, biometric validation of inmates such as voice print identification, allowed and disallowed contact lists, physical phone enclosures, and so on are all features in an ICS. These features allow call requests by inmates to be validated such that only valid requests, such as an inmate requesting a call to a family member evaluated as a non-threat, are allowed at the onset of the call request.
During a voice call itself, a common class of circumvention attempt involves the cooperation of an allowed called party. An inmate within the facility may contact an allowed called party without triggering any security issues in an ICS, and the called party may assist the inmate in contacting a third party for nefarious purposes using features commonly available to public telephone network customers. Three-way calling is a prime example: an allowed called party can establish a three-way call with a third party, which then allows an inmate and the third party to communicate using a call session originally established between the inmate and the allowed called party. Thus, contact between the inmate and the undesirable third party evades detection by the prison security apparatus.
In response, several schemes have been developed to detect three-way calling attempts. Several techniques fall under the umbrella of “sound detection,” in which sounds associated with three-way call activity are detected. One such method is the detection of a loud “clicking” sound called a “hookflash,” “switchhook,” or “flashhook” that is made when a called party switches to a different line to initiate a call session with a third party. To detect this sound, the energy of the call audio is used to detect a short burst of energy over the call session that exceeds a threshold. Another common scheme infers a three-way call attempt by detecting an extended period of silence. This detection scheme is based on the observation that the called party leaves the call session with the inmate for some period of time to initiate a call session with a third party, and thus the inmate call session may be silent for some amount of time.
As voice communication shifts towards Voice over Internet Protocol (VoIP), key validation and detection features have become jeopardized. VoIP operates on a “packet-switch” paradigm, in which packets representing samples of encoded voice are sent between speakers on a voice call where packets do not require a dedicated circuit to be established for the entire path between the call parties. VoIP packets are formatted according to a codec (a portmanteau of “coder-decoder”) which defines how sound is represented and sent within each VoIP packet.
In order to save network capacity when transmitting VoIP packets, an ICS may utilize codecs that compress sound data into a quality that is high enough to be understood by a human listener, but low enough that the network capacity required to transmit such packets is much lower than other, higher quality sound codecs. However, codecs that perform such compression of the audio may also hinder the use of techniques that depend on sound detection to function due to the lower quality of the audio. Therefore, a solution is required that allows high quality audio codecs to be used for sound-based validation and detection measures and lower quality audio codecs to be used for regular audio.